PHP Code Templates

PHP Code templates (pct) is a PHP library that parses and performs value substitution for PHP class templates.

Creating Templates

Defining a template involves creating a file that encapsulates a common structure marked up with areas where values should be substituted in order to create a concrete file that can perform (in the case of code) or provide something useful. PCT supports simple tag substitution as well as conditional and repeating sections.

Substitution Tags

To specify a spot in a template where a value is to be substituted, add a tag with the following grammar:

SUBSTITUTION_TAG        <- '/*#' SUBSTITUTION_EXPRESSION '#*/'
SUBSTITUTION_EXPRESSION <- (FILTER_EXPRESSION ('-' FILTER_EXPRESSION)* ':')?VARIABLE_NAME
FILTER_EXPRESSION       <- [a-zA-Z]+ ( '(' FILTER_PARAMETER (',' FILTER_PARAMETER)* ')' )?
FILTER_PARAMETER        <- .+
VARIABLE_NAME           <- [a-zA-Z]+ ('[' VARIABLE_INDEX ']')*
VARIABLE_INDEX          <- [a-zA-Z]+

Note that whitespace included between elements is for clarity only and should not be included when writing tags. The only exception to this is that any amount of whitespace can appear after the opening /*# and before the closing #*/.

Examples:

• /*# var #*/ -- Output the substitution value var
• /*# php:var #*/ -- Output the substitution value var using the php filter
• /*# join(,):var #*/ -- Output the substitution value var using the join filter with the ',' character as glue
• /*# each(php)-join(,):var #*/ -- Pass each value of var through the php filter and then join the resulting values using a comma
• /*# var[idx] #*/ -- Output the idx value of the array value var
• /*# var[idx][subidx] #*/ -- Nested indexes are supported too

Filters

There are a number of predefined filters for outputting substitution values.

• each(filter) Apply a filter to each value of an array substitution value.
• json Output the substitution value encoded as JSON.
• join(glue) Join all of the values of an array using glue and output the result.
• php Output the substitution value using var_export.
• xml Output the substitution with encoded XML entities. Note that this will not serialize an array or object as XML.

Filters can be layered by joining multiple filter expressions with the '-' character. Filters defined in this manner are evaluated left to right with each filter receiving the result of the previous filter as input.

Conditional Sections

Templates support conditional sections. These sections will only be output durring value substitution if the set of substitution values matches the conditional expression. Conditional sections have to following grammar:

IF_EXPRESSION   <- '#{ if' CONDITIONAL '\n' BLOCK
                   (('#{' / '#}{') ' elseif' CONDITIONAL '\n' BLOCK)*
                   (('#{' / '#}{') ' else' '\n' BLOCK)?
                   '#}'
CONDITIONAL     <- COMPARISON (('and' / 'or') COMPARISON)*
COMPARISON      <- OPERAND (UNARY_OPERATOR / BINARY_OPERATOR OPERAND)?
OPERAND         <- VARIABLE_NAME / NUMBER / STRING
VARIABLE_NAME   <- [a-zA-Z]+ ('[' VARIABLE_INDEX ']')*
VARIABLE_INDEX  <- [a-zA-Z]+
NUMBER          <- Any numeric string*
STRING          <- ('\'' / '"') .* ('\'' / '"')
BINARY_OPERATOR <- '=' / '!=' / '<' / '>' / '<=' / '>=' /
UNARY_OPERATOR  <- 'ISSET' / 'ISNOTSET'
BLOCK           <- PHP code with addition template syntax

When a comparision is defined as a single OPERAND without an operator, the boolean value of the resolved operand will be used to resolve the IF_EXPRESSION.

* as defined by is_numeric.

Example:

#{ if var[type] = 'list'
    // Handle a list
#}{ elseif var[type] = 'map'
   // Handle a map
#}{ else
   // Handle non-collection type
#}

Switch Block

In addition to if style conditional sections, a switch section can be used to substitute different content for different values of the same substitution variable.

Example:

#{ switch var
#| case 0
    // Handle case when var = 0
#| case > 0
    // Handle case when var > 0
#| case < 0
    // Handle case when var < 0
#}

The example for the if block could be rewritten as:

#{ switch var[type]
#| case 'list'
    // Handle a list
#| case 'map'
    // Handle a map
#| default
    / Handle non-collection type
#}

Switch cases do NOT fall through.

Repeating Sections

Repeating sections can be specified as follows:

#{ each <var> as <name> [<status>]
  <section>
#}

<var> must refer to an array substitution value. Within the repeated section, the current value of the array substitution value will be available for use by using the substitution value with name <name>

If a name is provided for the <status> variable, it will be populated as an array containing the following information:

• index: The current index of the iteration.
• first: Whether or not the iteration is on the first element.
• last: Whether or not the iteration is on the last element.
• has_next: Whether or not the iteration has another element after the current element.

Example

This example is a portion of the template used to create a persister object for model classes in the Clarinet ORM Project. The complete template can be found at https://github.com/pgraham/Clarinet/blob/master/src/persister/persister.tmlp.php

class /*# actor #*/ {

    // ...

    public function create(\/*# class #*/ $model) {

      if (!$this->validator->validate($model, $e)) {
        throw $e;
      }

      if ($model->get/*# id_property */() !== null) {
        return $model->get/*# id_property */();
      }

      #{ if beforeCreate
        $model->beforeCreate();
      #}

      try {
        $startTransaction = $this->_pdo->beginTransaction();

        $model->set/*# id_property */(self::CREATE_MARKER);

        $params = Array();
        #{ each properties as prop
          #{ if prop[type] = boolean
            $params['/*# prop[col] #*/'] = $model->get/*# prop[name] #*/() ? 1 : 0;
          #{ else
            $params['/*# prop[col] #*/'] = $model->get/*# prop[name] #*/();
          #}
        #}

        #{ each relationships as rel
          #{ if rel[type] = many-to-one
            // Populate /*# rel[rhs] #*/ parameter --------------------------------
            // ...
            // -------------------------------------------------------------------
          #}
        #}

        $this->_create->execute($params);

        $id = $this->transformer->idFromDb($this->_pdo->lastInsertId());
        $model->set/*# id_property */($id);
        $this->_cache[$id] = $model;

        #{ each collections as col
          $this->insertCollection_/*# col[property] #*/(
            $id,
            $model->get/*# col[property] #*/()
          );
        #}

        #{ each relationships as rel
          $related = $model->get/*# rel[lhsProperty] #*/();
          #{ if rel[type] = many-to-many
            // ...

          #{ elseif rel[type] = one-to-many
            // ...
          #}
        #}

        if ($startTransaction) {
          $this->_pdo->commit();
        }

        #{ if onCreate
          $model->onCreate();
        #} 

        return $id;
      } catch (PDOException $e) {
        $this->_pdo->rollback();
        $model->set/*# id_property */(null);

        $e = new PdoExceptionWrapper($e, '/*# class #*/');
        $e->setSql($sql, $params);
        throw $e;
      }
    }

    // ...

}

Value Substitution

Value substitution, referred to here after as template resolution (or more simply resolution) is the process of replacing all template tags with values so that a code template becomes an actual useful piece of code.

Templates can be resolved using a zpt\pct\TemplateResolver instance and invoking it's resolve($templatePath, $outputpath, $values); method.